The invention relates to a process for producing a casting mould with chemically bound moulding material using a pattern and a process for producing cast members.
A hollow space is produced in the moulding material, as part of a mould cavity for the cast member, and the mould cavity is filled with liquid metal, with a region which is influenced by the casting temperature being formed around the cast member in the moulding material. The man skilled in the art is aware of a number of different processes for producing cast members from liquid metal in a casting mould, wherein the mould cavity is formed using a pourable moulding sand with binding agent added thereto, and a model or pattern which is temporarily introduced into the moulding sand.
Thus for example in the sand casting hand moulding process, the process of making the mould from mould sand is effected using continuous-type mixers and manual operations, with a hand tamper, compressed air tamper or slinger device, giving a casting mould which can be used once. In the sand casting machine moulding process, casting moulds and cores are produced by means of mould or core blowing machines. Casting sand as the moulding material is introduced into moulds by shaking or jarring, pressing or squeezing under vacuum or by explosions, and thus compacted in the mould. Core moulds are generally shot out. The casting mould and the core can only be used once.
The shell moulding process uses heated metal patterns and core boxes for producing shell moulds and shell cores from sands which are bound with synthetic resin. In that case also, each shell and each core can only be used once.
Solid mould casting processes use patterns which can be used once and which are cut out of plastics foam and which are shaped in accordance with the hand moulding process but which remain in the casting mould. The moulding materials used here are foundery sands with for example cold-setting binders. That process is suitable both for the individual production of medium and large castings and also for mass production if foamed patterns are pre-fabricated on a mass production basis in special moulds.
Chemically bound sand moulds are successfully used in hand moulding, for individual production and for core production. In the realm of small-scale mass production, use is made of chemically bound sand moulds in the form of shells which are supported by cover shells or gas-pervious back-filling materials, for example by means of loose sand or steel shot.
In mass production processes, cast members are preferably made in iron moulds or green sand moulds. Factors that may be considered as advantages of green sand moulds over casting moulds comprising chemically bound sand are the low moulding material costs as well as the possibility of using production-tested automatic mould machines which permit short cycle times. However, the disadvantages of the green sand mould over chemically bound moulds predominate, namely:
high requirements in regard to quality of sand and binding agent; PA1 large amounts of moulding material required; PA1 binding agents are becoming scarce; PA1 expensive sand preparation and treatment, inter alia due to a large amount of space being required and long cooling sections; PA1 the need for two sand systems for the casting mould and the core; PA1 high energy expenditure; PA1 moulding and casting defects with just slight fluctuations in moulding material; PA1 large tolerance range; PA1 poor cast surfaces; PA1 a high level of cleaning expenditure; PA1 a high reject rate; PA1 the need for a high level of training of the operating personnel; PA1 serious environmental pollution. PA1 the mould and the core can be made from one moulding material; PA1 the quantity of moulding material introduced from the second phase on, is given by the casting process; PA1 the amount involved in the sand recovery operation is small; PA1 the quality of the sand is in most cases very good, due to the thermal loading thereon, and may even be better than new sand (new sand only needs to be added to make up for shrinkage or leakage); PA1 dumps are less heavily burdened; PA1 there is no longer the noise nuisance when knocking out; PA1 the recovery plant can be of low capacity; and PA1 the amount of liquid metal may in many cases be lower (riserless casting), which results in a reduction in the melting costs.
Having regard to those factors, the inventor now set himself the aim of providing a process for producing a casting mould of the kind referred to in the opening part of this specification, and thus cast members, by means of which it is possible to forego the use of clay-bound sands, in particular for the mass production of cast members, thereby avoiding the above-mentioned disadvantages, and providing a casting mould of adequate gas permeability, which is simple to produce, with a low level of consumption of moulding material, and inexpensive, and which also ensures a high degree of quality of casting with a low level of environmental pollution.